1. Field of the Invention
This invention relates to a molecular aligning method for liquid crystals and a liquid crystal device using said molecular aligning method.
2. Description of the Prior Art
At present, the liquid crystal display device (LCD) has been widely used in every possible field of application including, for example, wristwatch, game machine, color television and lap-top computers. Along with this trend, there is a rapidly growing demand for high performance LCDs. In order to respond to such a demand, high performance liquid crystal display devices have been developed including those using an active matrix display, ferroelectric liquid crystal display, super-twisted nematic liquid crystal display or the like.
As one of the essential factors for determining the performance of liquid crystal device reference can be made to alignment control technology. This technology is a process for aligning liquid crystal molecules in a definite direction all over the surface of a display device, on which the displaying quality thereof largely depends. If the alignment is not controlled satisfactorily, then critical defects such as, for example, uneven display, reduced contrast and reduced performance due to aging will take place. The importance of the alignment control technology is to be emphasized in common on not only the twisted nematic type (TN type) LCDs but also various types of high performance liquid crystal devices mentioned above, which means that this technology is becoming increasingly important.
Conventional methods for achieving the alignment control of liquid crystal molecules are the rubbing method in which after a polymer such as, for example, polyimide has been coated on the surface of an electrode to form a film thereon, the surface thus obtained is rubbed with cloth or the like, and the oblique evaporation method in which a material such as, for example, SiO.sub.2 is evaporated on the surface of an electrode from an oblique direction. Of these, the rubbing method is being mainly used because of its simplicity and low cost. Under such a circumstance that the trend to make liquid crystal display devices largely displayable in size and highly dense in structure is in progress, it becomes difficult to obtain a uniform and high quality display all over the surface thereof using the method in accordance with the prior art in which an alignment controlling film is formed and only rubbed. Namely, defect resulting from the generation of fiber dust from a rubbing cloth and difficulty in making the rubbing force uniform during the rubbing process, which had previously not been given much attention has begun to be examined closely accompanying the increasing trend to make the liquid crystal device of high performance. Particularly, none of the above-mentioned high performance liquid crystal display devices could be satisfactorily produced by following the methods of the prior art.
Referring to ferroelectric liquid crystal devices, particularly, different from previous twisted nematic ones, bistability of the alignment condition must be maintained. Accordingly, if the initial molecular alignment treatment is made excessively sufficient, the alignment condition will be stabilized in one direction only, so that the performance as the ferroelectric liquid crystal device is lost. On the other hand, if it is made insufficient, the alignment will become uneven. As a result, the alignment technology of ferroelectric liquid crystal device has an individuality and difficulty that can not possibly compare with those in accordance with the prior art.
The method disclosed in Japanese patent application Laid-Open No. 62-291621, Eguchi et al, uses an alignment controlling film of ferroelectric liquid crystal. A polymeric coating film made of a monomolecular film or a laminated monomolecular film of a polymeric compound having a hydrophilic part and a hydrophobic part in the molecule is employed. With this method, as Eguchi et al clearly showed, if rubbing is not made, a reduction in alignment controlling force results, thus the unevenness of alignment being produced. Also, Japanese patent application Laid-Open No. 63-126578, Uekita et al, points to a liquid crystal alignment film as one of applications of a composite part including a thin film formed by laminating a polymeric compound through the Langmuir-Blodgett method, but does not show the specificity of molecular alignment of ferroelectric liquid crystal.
Then, the ferroelectric liquid crystal device has a liquid crystal layer having a thickness which is extremely thin such as to be one-half or less that of the previous twisted nematic liquid crystal device, so that defect generation during manufacturing through the secondary treatment called rubbing process can be outstandingly increased. Accordingly, it is desired that the alignment control be achieved with no use of the rubbing process.